Hydraulic accumulators with housing opening closed by a cover are available commercially and are widely used in conjunction with hydraulic systems. A hydraulic accumulator of this type, for example, is marketed by Parker Hydraulics under the trade name ACP Series Accumulator.
Hydraulic accumulators of this kind are characterized by comparatively low production costs, since the cover closing the accumulator housing through formation of positively locking engagement of cover and the part of the accumulator housing surrounding it may be fastened by simple and efficient means. Specifically, the wall surrounding the cover, in the case of the piston-type accumulator the respective cylindrical tube, is deformed by rolling so that an annular ring projecting inward is formed and is engaged in an associated annular groove in the circumference of the cover.
This type of fastening of one or both housing cover(s) of conventional hydraulic accumulators is advantageous from the viewpoint of simple and cost-effective manufacture. However, it nevertheless creates problems with respect to the operating properties, and leads to difficulties in installation of such accumulators. While the positive locking of the cover and the wall element of the accumulator housing surrounding it effected by deformation rolling does ensure axial retention of the cover involved, this cover may nevertheless be twisted when torque of a certain strength relative to the longitudinal axis occurs. This twisting results in problems, for example, when torque is applied to the respective cover as a result of the forces of tightening screw connections in installing such accumulators in a hydraulic system by screw connections joining the cover on the fluid side, for example, to the outlet of a hydraulic pump. Forces, such as vibrations which occur during operation, may also cause torsion of the cover relative to the accumulator housing.